Imported Upstream version 0.27.1upstream/0.27.1

1 files changed, 1718 insertions, 0 deletions

diff --git a/glib/glib/gslice.c b/glib/glib/gslice.c
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+/* GLIB sliced memory - fast concurrent memory chunk allocator
+ * Copyright (C) 2005 Tim Janik
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+/* MT safe */
+
+#include "config.h"
+#include "glibconfig.h"
+
+#if     defined HAVE_POSIX_MEMALIGN && defined POSIX_MEMALIGN_WITH_COMPLIANT_ALLOCS
+#  define HAVE_COMPLIANT_POSIX_MEMALIGN 1
+#endif
+
+#if defined(HAVE_COMPLIANT_POSIX_MEMALIGN) && !defined(_XOPEN_SOURCE)
+#define _XOPEN_SOURCE 600       /* posix_memalign() */
+#endif
+#include <stdlib.h>             /* posix_memalign() */
+#include <string.h>
+#include <errno.h>
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>             /* sysconf() */
+#endif
+#ifdef G_OS_WIN32
+#include <windows.h>
+#include <process.h>
+#endif
+
+#include <stdio.h>              /* fputs/fprintf */
+
+#include "gslice.h"
+
+#include "gmain.h"
+#include "gmem.h"               /* gslice.h */
+#include "gstrfuncs.h"
+#include "gutils.h"
+#include "gtrashstack.h"
+#include "gtestutils.h"
+#include "gthread.h"
+#include "glib_trace.h"
+
+/**
+ * SECTION:memory_slices
+ * @title: Memory Slices
+ * @short_description: efficient way to allocate groups of equal-sized
+ *     chunks of memory
+ *
+ * Memory slices provide a space-efficient and multi-processing scalable
+ * way to allocate equal-sized pieces of memory, just like the original
+ * #GMemChunks (from GLib 2.8), while avoiding their excessive
+ * memory-waste, scalability and performance problems.
+ *
+ * To achieve these goals, the slice allocator uses a sophisticated,
+ * layered design that has been inspired by Bonwick's slab allocator
+ * <footnote><para>
+ * <ulink url="http://citeseer.ist.psu.edu/bonwick94slab.html">[Bonwick94]</ulink> Jeff Bonwick, The slab allocator: An object-caching kernel
+ * memory allocator. USENIX 1994, and
+ * <ulink url="http://citeseer.ist.psu.edu/bonwick01magazines.html">[Bonwick01]</ulink> Bonwick and Jonathan Adams, Magazines and vmem: Extending the
+ * slab allocator to many cpu's and arbitrary resources. USENIX 2001
+ * </para></footnote>.
+ * It uses posix_memalign() to optimize allocations of many equally-sized
+ * chunks, and has per-thread free lists (the so-called magazine layer)
+ * to quickly satisfy allocation requests of already known structure sizes.
+ * This is accompanied by extra caching logic to keep freed memory around
+ * for some time before returning it to the system. Memory that is unused
+ * due to alignment constraints is used for cache colorization (random
+ * distribution of chunk addresses) to improve CPU cache utilization. The
+ * caching layer of the slice allocator adapts itself to high lock contention
+ * to improve scalability.
+ *
+ * The slice allocator can allocate blocks as small as two pointers, and
+ * unlike malloc(), it does not reserve extra space per block. For large block
+ * sizes, g_slice_new() and g_slice_alloc() will automatically delegate to the
+ * system malloc() implementation. For newly written code it is recommended
+ * to use the new <literal>g_slice</literal> API instead of g_malloc() and
+ * friends, as long as objects are not resized during their lifetime and the
+ * object size used at allocation time is still available when freeing.
+ *
+ * <example>
+ * <title>Using the slice allocator</title>
+ * <programlisting>
+ * gchar *mem[10000];
+ * gint i;
+ *
+ * /&ast; Allocate 10000 blocks. &ast;/
+ * for (i = 0; i &lt; 10000; i++)
+ *   {
+ *     mem[i] = g_slice_alloc (50);
+ *
+ *     /&ast; Fill in the memory with some junk. &ast;/
+ *     for (j = 0; j &lt; 50; j++)
+ *       mem[i][j] = i * j;
+ *   }
+ *
+ * /&ast; Now free all of the blocks. &ast;/
+ * for (i = 0; i &lt; 10000; i++)
+ *   {
+ *     g_slice_free1 (50, mem[i]);
+ *   }
+ * </programlisting></example>
+ *
+ * <example>
+ * <title>Using the slice allocator with data structures</title>
+ * <programlisting>
+ * GRealArray *array;
+ *
+ * /&ast; Allocate one block, using the g_slice_new() macro. &ast;/
+ * array = g_slice_new (GRealArray);
+
+ * /&ast; We can now use array just like a normal pointer to a structure. &ast;/
+ * array->data            = NULL;
+ * array->len             = 0;
+ * array->alloc           = 0;
+ * array->zero_terminated = (zero_terminated ? 1 : 0);
+ * array->clear           = (clear ? 1 : 0);
+ * array->elt_size        = elt_size;
+ *
+ * /&ast; We can free the block, so it can be reused. &ast;/
+ * g_slice_free (GRealArray, array);
+ * </programlisting></example>
+ */
+
+/* the GSlice allocator is split up into 4 layers, roughly modelled after the slab
+ * allocator and magazine extensions as outlined in:
+ * + [Bonwick94] Jeff Bonwick, The slab allocator: An object-caching kernel
+ *   memory allocator. USENIX 1994, http://citeseer.ist.psu.edu/bonwick94slab.html
+ * + [Bonwick01] Bonwick and Jonathan Adams, Magazines and vmem: Extending the
+ *   slab allocator to many cpu's and arbitrary resources.
+ *   USENIX 2001, http://citeseer.ist.psu.edu/bonwick01magazines.html
+ * the layers are:
+ * - the thread magazines. for each (aligned) chunk size, a magazine (a list)
+ *   of recently freed and soon to be allocated chunks is maintained per thread.
+ *   this way, most alloc/free requests can be quickly satisfied from per-thread
+ *   free lists which only require one g_private_get() call to retrive the
+ *   thread handle.
+ * - the magazine cache. allocating and freeing chunks to/from threads only
+ *   occours at magazine sizes from a global depot of magazines. the depot
+ *   maintaines a 15 second working set of allocated magazines, so full
+ *   magazines are not allocated and released too often.
+ *   the chunk size dependent magazine sizes automatically adapt (within limits,
+ *   see [3]) to lock contention to properly scale performance across a variety
+ *   of SMP systems.
+ * - the slab allocator. this allocator allocates slabs (blocks of memory) close
+ *   to the system page size or multiples thereof which have to be page aligned.
+ *   the blocks are divided into smaller chunks which are used to satisfy
+ *   allocations from the upper layers. the space provided by the reminder of
+ *   the chunk size division is used for cache colorization (random distribution
+ *   of chunk addresses) to improve processor cache utilization. multiple slabs
+ *   with the same chunk size are kept in a partially sorted ring to allow O(1)
+ *   freeing and allocation of chunks (as long as the allocation of an entirely
+ *   new slab can be avoided).
+ * - the page allocator. on most modern systems, posix_memalign(3) or
+ *   memalign(3) should be available, so this is used to allocate blocks with
+ *   system page size based alignments and sizes or multiples thereof.
+ *   if no memalign variant is provided, valloc() is used instead and
+ *   block sizes are limited to the system page size (no multiples thereof).
+ *   as a fallback, on system without even valloc(), a malloc(3)-based page
+ *   allocator with alloc-only behaviour is used.
+ *
+ * NOTES:
+ * [1] some systems memalign(3) implementations may rely on boundary tagging for
+ *     the handed out memory chunks. to avoid excessive page-wise fragmentation,
+ *     we reserve 2 * sizeof (void*) per block size for the systems memalign(3),
+ *     specified in NATIVE_MALLOC_PADDING.
+ * [2] using the slab allocator alone already provides for a fast and efficient
+ *     allocator, it doesn't properly scale beyond single-threaded uses though.
+ *     also, the slab allocator implements eager free(3)-ing, i.e. does not
+ *     provide any form of caching or working set maintenance. so if used alone,
+ *     it's vulnerable to trashing for sequences of balanced (alloc, free) pairs
+ *     at certain thresholds.
+ * [3] magazine sizes are bound by an implementation specific minimum size and
+ *     a chunk size specific maximum to limit magazine storage sizes to roughly
+ *     16KB.
+ * [4] allocating ca. 8 chunks per block/page keeps a good balance between
+ *     external and internal fragmentation (<= 12.5%). [Bonwick94]
+ */
+
+/* --- macros and constants --- */
+#define LARGEALIGNMENT          (256)
+#define P2ALIGNMENT             (2 * sizeof (gsize))                            /* fits 2 pointers (assumed to be 2 * GLIB_SIZEOF_SIZE_T below) */
+#define ALIGN(size, base)       ((base) * (gsize) (((size) + (base) - 1) / (base)))
+#define NATIVE_MALLOC_PADDING   P2ALIGNMENT                                     /* per-page padding left for native malloc(3) see [1] */
+#define SLAB_INFO_SIZE          P2ALIGN (sizeof (SlabInfo) + NATIVE_MALLOC_PADDING)
+#define MAX_MAGAZINE_SIZE       (256)                                           /* see [3] and allocator_get_magazine_threshold() for this */
+#define MIN_MAGAZINE_SIZE       (4)
+#define MAX_STAMP_COUNTER       (7)                                             /* distributes the load of gettimeofday() */
+#define MAX_SLAB_CHUNK_SIZE(al) (((al)->max_page_size - SLAB_INFO_SIZE) / 8)    /* we want at last 8 chunks per page, see [4] */
+#define MAX_SLAB_INDEX(al)      (SLAB_INDEX (al, MAX_SLAB_CHUNK_SIZE (al)) + 1)
+#define SLAB_INDEX(al, asize)   ((asize) / P2ALIGNMENT - 1)                     /* asize must be P2ALIGNMENT aligned */
+#define SLAB_CHUNK_SIZE(al, ix) (((ix) + 1) * P2ALIGNMENT)
+#define SLAB_BPAGE_SIZE(al,csz) (8 * (csz) + SLAB_INFO_SIZE)
+
+/* optimized version of ALIGN (size, P2ALIGNMENT) */
+#if     GLIB_SIZEOF_SIZE_T * 2 == 8  /* P2ALIGNMENT */
+#define P2ALIGN(size)   (((size) + 0x7) & ~(gsize) 0x7)
+#elif   GLIB_SIZEOF_SIZE_T * 2 == 16 /* P2ALIGNMENT */
+#define P2ALIGN(size)   (((size) + 0xf) & ~(gsize) 0xf)
+#else
+#define P2ALIGN(size)   ALIGN (size, P2ALIGNMENT)
+#endif
+
+/* special helpers to avoid gmessage.c dependency */
+static void mem_error (const char *format, ...) G_GNUC_PRINTF (1,2);
+#define mem_assert(cond)    do { if (G_LIKELY (cond)) ; else mem_error ("assertion failed: %s", #cond); } while (0)
+
+/* --- structures --- */
+typedef struct _ChunkLink      ChunkLink;
+typedef struct _SlabInfo       SlabInfo;
+typedef struct _CachedMagazine CachedMagazine;
+struct _ChunkLink {
+  ChunkLink *next;
+  ChunkLink *data;
+};
+struct _SlabInfo {
+  ChunkLink *chunks;
+  guint n_allocated;
+  SlabInfo *next, *prev;
+};
+typedef struct {
+  ChunkLink *chunks;
+  gsize      count;                     /* approximative chunks list length */
+} Magazine;
+typedef struct {
+  Magazine   *magazine1;                /* array of MAX_SLAB_INDEX (allocator) */
+  Magazine   *magazine2;                /* array of MAX_SLAB_INDEX (allocator) */
+} ThreadMemory;
+typedef struct {
+  gboolean always_malloc;
+  gboolean bypass_magazines;
+  gboolean debug_blocks;
+  gsize    working_set_msecs;
+  guint    color_increment;
+} SliceConfig;
+typedef struct {
+  /* const after initialization */
+  gsize         min_page_size, max_page_size;
+  SliceConfig   config;
+  gsize         max_slab_chunk_size_for_magazine_cache;
+  /* magazine cache */
+  GMutex        magazine_mutex;
+  ChunkLink   **magazines;                /* array of MAX_SLAB_INDEX (allocator) */
+  guint        *contention_counters;      /* array of MAX_SLAB_INDEX (allocator) */
+  gint          mutex_counter;
+  guint         stamp_counter;
+  guint         last_stamp;
+  /* slab allocator */
+  GMutex        slab_mutex;
+  SlabInfo    **slab_stack;                /* array of MAX_SLAB_INDEX (allocator) */
+  guint        color_accu;
+} Allocator;
+
+/* --- g-slice prototypes --- */
+static gpointer     slab_allocator_alloc_chunk       (gsize      chunk_size);
+static void         slab_allocator_free_chunk        (gsize      chunk_size,
+                                                      gpointer   mem);
+static void         private_thread_memory_cleanup    (gpointer   data);
+static gpointer     allocator_memalign               (gsize      alignment,
+                                                      gsize      memsize);
+static void         allocator_memfree                (gsize      memsize,
+                                                      gpointer   mem);
+static inline void  magazine_cache_update_stamp      (void);
+static inline gsize allocator_get_magazine_threshold (Allocator *allocator,
+                                                      guint      ix);
+
+/* --- g-slice memory checker --- */
+static void     smc_notify_alloc  (void   *pointer,
+                                   size_t  size);
+static int      smc_notify_free   (void   *pointer,
+                                   size_t  size);
+
+/* --- variables --- */
+static GPrivate    private_thread_memory = G_PRIVATE_INIT (private_thread_memory_cleanup);
+static gsize       sys_page_size = 0;
+static Allocator   allocator[1] = { { 0, }, };
+static SliceConfig slice_config = {
+  FALSE,        /* always_malloc */
+  FALSE,        /* bypass_magazines */
+  FALSE,        /* debug_blocks */
+  15 * 1000,    /* working_set_msecs */
+  1,            /* color increment, alt: 0x7fffffff */
+};
+static GMutex      smc_tree_mutex; /* mutex for G_SLICE=debug-blocks */
+
+/* --- auxiliary funcitons --- */
+void
+g_slice_set_config (GSliceConfig ckey,
+                    gint64       value)
+{
+  g_return_if_fail (sys_page_size == 0);
+  switch (ckey)
+    {
+    case G_SLICE_CONFIG_ALWAYS_MALLOC:
+      slice_config.always_malloc = value != 0;
+      break;
+    case G_SLICE_CONFIG_BYPASS_MAGAZINES:
+      slice_config.bypass_magazines = value != 0;
+      break;
+    case G_SLICE_CONFIG_WORKING_SET_MSECS:
+      slice_config.working_set_msecs = value;
+      break;
+    case G_SLICE_CONFIG_COLOR_INCREMENT:
+      slice_config.color_increment = value;
+    default: ;
+    }
+}
+
+gint64
+g_slice_get_config (GSliceConfig ckey)
+{
+  switch (ckey)
+    {
+    case G_SLICE_CONFIG_ALWAYS_MALLOC:
+      return slice_config.always_malloc;
+    case G_SLICE_CONFIG_BYPASS_MAGAZINES:
+      return slice_config.bypass_magazines;
+    case G_SLICE_CONFIG_WORKING_SET_MSECS:
+      return slice_config.working_set_msecs;
+    case G_SLICE_CONFIG_CHUNK_SIZES:
+      return MAX_SLAB_INDEX (allocator);
+    case G_SLICE_CONFIG_COLOR_INCREMENT:
+      return slice_config.color_increment;
+    default:
+      return 0;
+    }
+}
+
+gint64*
+g_slice_get_config_state (GSliceConfig ckey,
+                          gint64       address,
+                          guint       *n_values)
+{
+  guint i = 0;
+  g_return_val_if_fail (n_values != NULL, NULL);
+  *n_values = 0;
+  switch (ckey)
+    {
+      gint64 array[64];
+    case G_SLICE_CONFIG_CONTENTION_COUNTER:
+      array[i++] = SLAB_CHUNK_SIZE (allocator, address);
+      array[i++] = allocator->contention_counters[address];
+      array[i++] = allocator_get_magazine_threshold (allocator, address);
+      *n_values = i;
+      return g_memdup (array, sizeof (array[0]) * *n_values);
+    default:
+      return NULL;
+    }
+}
+
+static void
+slice_config_init (SliceConfig *config)
+{
+  const gchar *val;
+
+  *config = slice_config;
+
+  val = getenv ("G_SLICE");
+  if (val != NULL)
+    {
+      gint flags;
+      const GDebugKey keys[] = {
+        { "always-malloc", 1 << 0 },
+        { "debug-blocks",  1 << 1 },
+      };
+
+      flags = g_parse_debug_string (val, keys, G_N_ELEMENTS (keys));
+      if (flags & (1 << 0))
+        config->always_malloc = TRUE;
+      if (flags & (1 << 1))
+        config->debug_blocks = TRUE;
+    }
+}
+
+static void
+g_slice_init_nomessage (void)
+{
+  /* we may not use g_error() or friends here */
+  mem_assert (sys_page_size == 0);
+  mem_assert (MIN_MAGAZINE_SIZE >= 4);
+
+#ifdef G_OS_WIN32
+  {
+    SYSTEM_INFO system_info;
+    GetSystemInfo (&system_info);
+    sys_page_size = system_info.dwPageSize;
+  }
+#else
+  sys_page_size = sysconf (_SC_PAGESIZE); /* = sysconf (_SC_PAGE_SIZE); = getpagesize(); */
+#endif
+  mem_assert (sys_page_size >= 2 * LARGEALIGNMENT);
+  mem_assert ((sys_page_size & (sys_page_size - 1)) == 0);
+  slice_config_init (&allocator->config);
+  allocator->min_page_size = sys_page_size;
+#if HAVE_COMPLIANT_POSIX_MEMALIGN || HAVE_MEMALIGN
+  /* allow allocation of pages up to 8KB (with 8KB alignment).
+   * this is useful because many medium to large sized structures
+   * fit less than 8 times (see [4]) into 4KB pages.
+   * we allow very small page sizes here, to reduce wastage in
+   * threads if only small allocations are required (this does
+   * bear the risk of increasing allocation times and fragmentation
+   * though).
+   */
+  allocator->min_page_size = MAX (allocator->min_page_size, 4096);
+  allocator->max_page_size = MAX (allocator->min_page_size, 8192);
+  allocator->min_page_size = MIN (allocator->min_page_size, 128);
+#else
+  /* we can only align to system page size */
+  allocator->max_page_size = sys_page_size;
+#endif
+  if (allocator->config.always_malloc)
+    {
+      allocator->contention_counters = NULL;
+      allocator->magazines = NULL;
+      allocator->slab_stack = NULL;
+    }
+  else
+    {
+      allocator->contention_counters = g_new0 (guint, MAX_SLAB_INDEX (allocator));
+      allocator->magazines = g_new0 (ChunkLink*, MAX_SLAB_INDEX (allocator));
+      allocator->slab_stack = g_new0 (SlabInfo*, MAX_SLAB_INDEX (allocator));
+    }
+
+  g_mutex_init (&allocator->magazine_mutex);
+  allocator->mutex_counter = 0;
+  allocator->stamp_counter = MAX_STAMP_COUNTER; /* force initial update */
+  allocator->last_stamp = 0;
+  g_mutex_init (&allocator->slab_mutex);
+  allocator->color_accu = 0;
+  magazine_cache_update_stamp();
+  /* values cached for performance reasons */
+  allocator->max_slab_chunk_size_for_magazine_cache = MAX_SLAB_CHUNK_SIZE (allocator);
+  if (allocator->config.always_malloc || allocator->config.bypass_magazines)
+    allocator->max_slab_chunk_size_for_magazine_cache = 0;      /* non-optimized cases */
+}
+
+static inline guint
+allocator_categorize (gsize aligned_chunk_size)
+{
+  /* speed up the likely path */
+  if (G_LIKELY (aligned_chunk_size && aligned_chunk_size <= allocator->max_slab_chunk_size_for_magazine_cache))
+    return 1;           /* use magazine cache */
+
+  if (!allocator->config.always_malloc &&
+      aligned_chunk_size &&
+      aligned_chunk_size <= MAX_SLAB_CHUNK_SIZE (allocator))
+    {
+      if (allocator->config.bypass_magazines)
+        return 2;       /* use slab allocator, see [2] */
+      return 1;         /* use magazine cache */
+    }
+  return 0;             /* use malloc() */
+}
+
+static inline void
+g_mutex_lock_a (GMutex *mutex,
+                guint  *contention_counter)
+{
+  gboolean contention = FALSE;
+  if (!g_mutex_trylock (mutex))
+    {
+      g_mutex_lock (mutex);
+      contention = TRUE;
+    }
+  if (contention)
+    {
+      allocator->mutex_counter++;
+      if (allocator->mutex_counter >= 1)        /* quickly adapt to contention */
+        {
+          allocator->mutex_counter = 0;
+          *contention_counter = MIN (*contention_counter + 1, MAX_MAGAZINE_SIZE);
+        }
+    }
+  else /* !contention */
+    {
+      allocator->mutex_counter--;
+      if (allocator->mutex_counter < -11)       /* moderately recover magazine sizes */
+        {
+          allocator->mutex_counter = 0;
+          *contention_counter = MAX (*contention_counter, 1) - 1;
+        }
+    }
+}
+
+static inline ThreadMemory*
+thread_memory_from_self (void)
+{
+  ThreadMemory *tmem = g_private_get (&private_thread_memory);
+  if (G_UNLIKELY (!tmem))
+    {
+      static GMutex init_mutex;
+      guint n_magazines;
+
+      g_mutex_lock (&init_mutex);
+      if G_UNLIKELY (sys_page_size == 0)
+        g_slice_init_nomessage ();
+      g_mutex_unlock (&init_mutex);
+
+      n_magazines = MAX_SLAB_INDEX (allocator);
+      tmem = g_malloc0 (sizeof (ThreadMemory) + sizeof (Magazine) * 2 * n_magazines);
+      tmem->magazine1 = (Magazine*) (tmem + 1);
+      tmem->magazine2 = &tmem->magazine1[n_magazines];
+      g_private_set (&private_thread_memory, tmem);
+    }
+  return tmem;
+}
+
+static inline ChunkLink*
+magazine_chain_pop_head (ChunkLink **magazine_chunks)
+{
+  /* magazine chains are linked via ChunkLink->next.
+   * each ChunkLink->data of the toplevel chain may point to a subchain,
+   * linked via ChunkLink->next. ChunkLink->data of the subchains just
+   * contains uninitialized junk.
+   */
+  ChunkLink *chunk = (*magazine_chunks)->data;
+  if (G_UNLIKELY (chunk))
+    {
+      /* allocating from freed list */
+      (*magazine_chunks)->data = chunk->next;
+    }
+  else
+    {
+      chunk = *magazine_chunks;
+      *magazine_chunks = chunk->next;
+    }
+  return chunk;
+}
+
+#if 0 /* useful for debugging */
+static guint
+magazine_count (ChunkLink *head)
+{
+  guint count = 0;
+  if (!head)
+    return 0;
+  while (head)
+    {
+      ChunkLink *child = head->data;
+      count += 1;
+      for (child = head->data; child; child = child->next)
+        count += 1;
+      head = head->next;
+    }
+  return count;
+}
+#endif
+
+static inline gsize
+allocator_get_magazine_threshold (Allocator *allocator,
+                                  guint      ix)
+{
+  /* the magazine size calculated here has a lower bound of MIN_MAGAZINE_SIZE,
+   * which is required by the implementation. also, for moderately sized chunks
+   * (say >= 64 bytes), magazine sizes shouldn't be much smaller then the number
+   * of chunks available per page/2 to avoid excessive traffic in the magazine
+   * cache for small to medium sized structures.
+   * the upper bound of the magazine size is effectively provided by
+   * MAX_MAGAZINE_SIZE. for larger chunks, this number is scaled down so that
+   * the content of a single magazine doesn't exceed ca. 16KB.
+   */
+  gsize chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
+  guint threshold = MAX (MIN_MAGAZINE_SIZE, allocator->max_page_size / MAX (5 * chunk_size, 5 * 32));
+  guint contention_counter = allocator->contention_counters[ix];
+  if (G_UNLIKELY (contention_counter))  /* single CPU bias */
+    {
+      /* adapt contention counter thresholds to chunk sizes */
+      contention_counter = contention_counter * 64 / chunk_size;
+      threshold = MAX (threshold, contention_counter);
+    }
+  return threshold;
+}
+
+/* --- magazine cache --- */
+static inline void
+magazine_cache_update_stamp (void)
+{
+  if (allocator->stamp_counter >= MAX_STAMP_COUNTER)
+    {
+      GTimeVal tv;
+      g_get_current_time (&tv);
+      allocator->last_stamp = tv.tv_sec * 1000 + tv.tv_usec / 1000; /* milli seconds */
+      allocator->stamp_counter = 0;
+    }
+  else
+    allocator->stamp_counter++;
+}
+
+static inline ChunkLink*
+magazine_chain_prepare_fields (ChunkLink *magazine_chunks)
+{
+  ChunkLink *chunk1;
+  ChunkLink *chunk2;
+  ChunkLink *chunk3;
+  ChunkLink *chunk4;
+  /* checked upon initialization: mem_assert (MIN_MAGAZINE_SIZE >= 4); */
+  /* ensure a magazine with at least 4 unused data pointers */
+  chunk1 = magazine_chain_pop_head (&magazine_chunks);
+  chunk2 = magazine_chain_pop_head (&magazine_chunks);
+  chunk3 = magazine_chain_pop_head (&magazine_chunks);
+  chunk4 = magazine_chain_pop_head (&magazine_chunks);
+  chunk4->next = magazine_chunks;
+  chunk3->next = chunk4;
+  chunk2->next = chunk3;
+  chunk1->next = chunk2;
+  return chunk1;
+}
+
+/* access the first 3 fields of a specially prepared magazine chain */
+#define magazine_chain_prev(mc)         ((mc)->data)
+#define magazine_chain_stamp(mc)        ((mc)->next->data)
+#define magazine_chain_uint_stamp(mc)   GPOINTER_TO_UINT ((mc)->next->data)
+#define magazine_chain_next(mc)         ((mc)->next->next->data)
+#define magazine_chain_count(mc)        ((mc)->next->next->next->data)
+
+static void
+magazine_cache_trim (Allocator *allocator,
+                     guint      ix,
+                     guint      stamp)
+{
+  /* g_mutex_lock (allocator->mutex); done by caller */
+  /* trim magazine cache from tail */
+  ChunkLink *current = magazine_chain_prev (allocator->magazines[ix]);
+  ChunkLink *trash = NULL;
+  while (ABS (stamp - magazine_chain_uint_stamp (current)) >= allocator->config.working_set_msecs)
+    {
+      /* unlink */
+      ChunkLink *prev = magazine_chain_prev (current);
+      ChunkLink *next = magazine_chain_next (current);
+      magazine_chain_next (prev) = next;
+      magazine_chain_prev (next) = prev;
+      /* clear special fields, put on trash stack */
+      magazine_chain_next (current) = NULL;
+      magazine_chain_count (current) = NULL;
+      magazine_chain_stamp (current) = NULL;
+      magazine_chain_prev (current) = trash;
+      trash = current;
+      /* fixup list head if required */
+      if (current == allocator->magazines[ix])
+        {
+          allocator->magazines[ix] = NULL;
+          break;
+        }
+      current = prev;
+    }
+  g_mutex_unlock (&allocator->magazine_mutex);
+  /* free trash */
+  if (trash)
+    {
+      const gsize chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
+      g_mutex_lock (&allocator->slab_mutex);
+      while (trash)
+        {
+          current = trash;
+          trash = magazine_chain_prev (current);
+          magazine_chain_prev (current) = NULL; /* clear special field */
+          while (current)
+            {
+              ChunkLink *chunk = magazine_chain_pop_head (&current);
+              slab_allocator_free_chunk (chunk_size, chunk);
+            }
+        }
+      g_mutex_unlock (&allocator->slab_mutex);
+    }
+}
+
+static void
+magazine_cache_push_magazine (guint      ix,
+                              ChunkLink *magazine_chunks,
+                              gsize      count) /* must be >= MIN_MAGAZINE_SIZE */
+{
+  ChunkLink *current = magazine_chain_prepare_fields (magazine_chunks);
+  ChunkLink *next, *prev;
+  g_mutex_lock (&allocator->magazine_mutex);
+  /* add magazine at head */
+  next = allocator->magazines[ix];
+  if (next)
+    prev = magazine_chain_prev (next);
+  else
+    next = prev = current;
+  magazine_chain_next (prev) = current;
+  magazine_chain_prev (next) = current;
+  magazine_chain_prev (current) = prev;
+  magazine_chain_next (current) = next;
+  magazine_chain_count (current) = (gpointer) count;
+  /* stamp magazine */
+  magazine_cache_update_stamp();
+  magazine_chain_stamp (current) = GUINT_TO_POINTER (allocator->last_stamp);
+  allocator->magazines[ix] = current;
+  /* free old magazines beyond a certain threshold */
+  magazine_cache_trim (allocator, ix, allocator->last_stamp);
+  /* g_mutex_unlock (allocator->mutex); was done by magazine_cache_trim() */
+}
+
+static ChunkLink*
+magazine_cache_pop_magazine (guint  ix,
+                             gsize *countp)
+{
+  g_mutex_lock_a (&allocator->magazine_mutex, &allocator->contention_counters[ix]);
+  if (!allocator->magazines[ix])
+    {
+      guint magazine_threshold = allocator_get_magazine_threshold (allocator, ix);
+      gsize i, chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
+      ChunkLink *chunk, *head;
+      g_mutex_unlock (&allocator->magazine_mutex);
+      g_mutex_lock (&allocator->slab_mutex);
+      head = slab_allocator_alloc_chunk (chunk_size);
+      head->data = NULL;
+      chunk = head;
+      for (i = 1; i < magazine_threshold; i++)
+        {
+          chunk->next = slab_allocator_alloc_chunk (chunk_size);
+          chunk = chunk->next;
+          chunk->data = NULL;
+        }
+      chunk->next = NULL;
+      g_mutex_unlock (&allocator->slab_mutex);
+      *countp = i;
+      return head;
+    }
+  else
+    {
+      ChunkLink *current = allocator->magazines[ix];
+      ChunkLink *prev = magazine_chain_prev (current);
+      ChunkLink *next = magazine_chain_next (current);
+      /* unlink */
+      magazine_chain_next (prev) = next;
+      magazine_chain_prev (next) = prev;
+      allocator->magazines[ix] = next == current ? NULL : next;
+      g_mutex_unlock (&allocator->magazine_mutex);
+      /* clear special fields and hand out */
+      *countp = (gsize) magazine_chain_count (current);
+      magazine_chain_prev (current) = NULL;
+      magazine_chain_next (current) = NULL;
+      magazine_chain_count (current) = NULL;
+      magazine_chain_stamp (current) = NULL;
+      return current;
+    }
+}
+
+/* --- thread magazines --- */
+static void
+private_thread_memory_cleanup (gpointer data)
+{
+  ThreadMemory *tmem = data;
+  const guint n_magazines = MAX_SLAB_INDEX (allocator);
+  guint ix;
+  for (ix = 0; ix < n_magazines; ix++)
+    {
+      Magazine *mags[2];
+      guint j;
+      mags[0] = &tmem->magazine1[ix];
+      mags[1] = &tmem->magazine2[ix];
+      for (j = 0; j < 2; j++)
+        {
+          Magazine *mag = mags[j];
+          if (mag->count >= MIN_MAGAZINE_SIZE)
+            magazine_cache_push_magazine (ix, mag->chunks, mag->count);
+          else
+            {
+              const gsize chunk_size = SLAB_CHUNK_SIZE (allocator, ix);
+              g_mutex_lock (&allocator->slab_mutex);
+              while (mag->chunks)
+                {
+                  ChunkLink *chunk = magazine_chain_pop_head (&mag->chunks);
+                  slab_allocator_free_chunk (chunk_size, chunk);
+                }
+              g_mutex_unlock (&allocator->slab_mutex);
+            }
+        }
+    }
+  g_free (tmem);
+}
+
+static void
+thread_memory_magazine1_reload (ThreadMemory *tmem,
+                                guint         ix)
+{
+  Magazine *mag = &tmem->magazine1[ix];
+  mem_assert (mag->chunks == NULL); /* ensure that we may reset mag->count */
+  mag->count = 0;
+  mag->chunks = magazine_cache_pop_magazine (ix, &mag->count);
+}
+
+static void
+thread_memory_magazine2_unload (ThreadMemory *tmem,
+                                guint         ix)
+{
+  Magazine *mag = &tmem->magazine2[ix];
+  magazine_cache_push_magazine (ix, mag->chunks, mag->count);
+  mag->chunks = NULL;
+  mag->count = 0;
+}
+
+static inline void
+thread_memory_swap_magazines (ThreadMemory *tmem,
+                              guint         ix)
+{
+  Magazine xmag = tmem->magazine1[ix];
+  tmem->magazine1[ix] = tmem->magazine2[ix];
+  tmem->magazine2[ix] = xmag;
+}
+
+static inline gboolean
+thread_memory_magazine1_is_empty (ThreadMemory *tmem,
+                                  guint         ix)
+{
+  return tmem->magazine1[ix].chunks == NULL;
+}
+
+static inline gboolean
+thread_memory_magazine2_is_full (ThreadMemory *tmem,
+                                 guint         ix)
+{
+  return tmem->magazine2[ix].count >= allocator_get_magazine_threshold (allocator, ix);
+}
+
+static inline gpointer
+thread_memory_magazine1_alloc (ThreadMemory *tmem,
+                               guint         ix)
+{
+  Magazine *mag = &tmem->magazine1[ix];
+  ChunkLink *chunk = magazine_chain_pop_head (&mag->chunks);
+  if (G_LIKELY (mag->count > 0))
+    mag->count--;
+  return chunk;
+}
+
+static inline void
+thread_memory_magazine2_free (ThreadMemory *tmem,
+                              guint         ix,
+                              gpointer      mem)
+{
+  Magazine *mag = &tmem->magazine2[ix];
+  ChunkLink *chunk = mem;
+  chunk->data = NULL;
+  chunk->next = mag->chunks;
+  mag->chunks = chunk;
+  mag->count++;
+}
+
+/* --- API functions --- */
+
+/**
+ * g_slice_new:
+ * @type: the type to allocate, typically a structure name
+ *
+ * A convenience macro to allocate a block of memory from the
+ * slice allocator.
+ *
+ * It calls g_slice_alloc() with <literal>sizeof (@type)</literal>
+ * and casts the returned pointer to a pointer of the given type,
+ * avoiding a type cast in the source code.
+ * Note that the underlying slice allocation mechanism can
+ * be changed with the <link linkend="G_SLICE">G_SLICE=always-malloc</link>
+ * environment variable.
+ *
+ * Returns: a pointer to the allocated block, cast to a pointer to @type
+ *
+ * Since: 2.10
+ */
+
+/**
+ * g_slice_new0:
+ * @type: the type to allocate, typically a structure name
+ *
+ * A convenience macro to allocate a block of memory from the
+ * slice allocator and set the memory to 0.
+ *
+ * It calls g_slice_alloc0() with <literal>sizeof (@type)</literal>
+ * and casts the returned pointer to a pointer of the given type,
+ * avoiding a type cast in the source code.
+ * Note that the underlying slice allocation mechanism can
+ * be changed with the <link linkend="G_SLICE">G_SLICE=always-malloc</link>
+ * environment variable.
+ *
+ * Since: 2.10
+ */
+
+/**
+ * g_slice_dup:
+ * @type: the type to duplicate, typically a structure name
+ * @mem: the memory to copy into the allocated block
+ *
+ * A convenience macro to duplicate a block of memory using
+ * the slice allocator.
+ *
+ * It calls g_slice_copy() with <literal>sizeof (@type)</literal>
+ * and casts the returned pointer to a pointer of the given type,
+ * avoiding a type cast in the source code.
+ * Note that the underlying slice allocation mechanism can
+ * be changed with the <link linkend="G_SLICE">G_SLICE=always-malloc</link>
+ * environment variable.
+ *
+ * Returns: a pointer to the allocated block, cast to a pointer to @type
+ *
+ * Since: 2.14
+ */
+
+/**
+ * g_slice_free:
+ * @type: the type of the block to free, typically a structure name
+ * @mem: a pointer to the block to free
+ *
+ * A convenience macro to free a block of memory that has
+ * been allocated from the slice allocator.
+ *
+ * It calls g_slice_free1() using <literal>sizeof (type)</literal>
+ * as the block size.
+ * Note that the exact release behaviour can be changed with the
+ * <link linkend="G_DEBUG">G_DEBUG=gc-friendly</link> environment
+ * variable, also see <link linkend="G_SLICE">G_SLICE</link> for
+ * related debugging options.
+ *
+ * Since: 2.10
+ */
+
+/**
+ * g_slice_free_chain:
+ * @type: the type of the @mem_chain blocks
+ * @mem_chain: a pointer to the first block of the chain
+ * @next: the field name of the next pointer in @type
+ *
+ * Frees a linked list of memory blocks of structure type @type.
+ * The memory blocks must be equal-sized, allocated via
+ * g_slice_alloc() or g_slice_alloc0() and linked together by
+ * a @next pointer (similar to #GSList). The name of the
+ * @next field in @type is passed as third argument.
+ * Note that the exact release behaviour can be changed with the
+ * <link linkend="G_DEBUG">G_DEBUG=gc-friendly</link> environment
+ * variable, also see <link linkend="G_SLICE">G_SLICE</link> for
+ * related debugging options.
+ *
+ * Since: 2.10
+ */
+
+/**
+ * g_slice_alloc:
+ * @block_size: the number of bytes to allocate
+ *
+ * Allocates a block of memory from the slice allocator.
+ * The block adress handed out can be expected to be aligned
+ * to at least <literal>1 * sizeof (void*)</literal>,
+ * though in general slices are 2 * sizeof (void*) bytes aligned,
+ * if a malloc() fallback implementation is used instead,
+ * the alignment may be reduced in a libc dependent fashion.
+ * Note that the underlying slice allocation mechanism can
+ * be changed with the <link linkend="G_SLICE">G_SLICE=always-malloc</link>
+ * environment variable.
+ *
+ * Returns: a pointer to the allocated memory block
+ *
+ * Since: 2.10
+ */
+gpointer
+g_slice_alloc (gsize mem_size)
+{
+  ThreadMemory *tmem;
+  gsize chunk_size;
+  gpointer mem;
+  guint acat;
+
+  /* This gets the private structure for this thread.  If the private
+   * structure does not yet exist, it is created.
+   *
+   * This has a side effect of causing GSlice to be initialised, so it
+   * must come first.
+   */
+  tmem = thread_memory_from_self ();
+
+  chunk_size = P2ALIGN (mem_size);
+  acat = allocator_categorize (chunk_size);
+  if (G_LIKELY (acat == 1))     /* allocate through magazine layer */
+    {
+      guint ix = SLAB_INDEX (allocator, chunk_size);
+      if (G_UNLIKELY (thread_memory_magazine1_is_empty (tmem, ix)))
+        {
+          thread_memory_swap_magazines (tmem, ix);
+          if (G_UNLIKELY (thread_memory_magazine1_is_empty (tmem, ix)))
+            thread_memory_magazine1_reload (tmem, ix);
+        }
+      mem = thread_memory_magazine1_alloc (tmem, ix);
+    }
+  else if (acat == 2)           /* allocate through slab allocator */
+    {
+      g_mutex_lock (&allocator->slab_mutex);
+      mem = slab_allocator_alloc_chunk (chunk_size);
+      g_mutex_unlock (&allocator->slab_mutex);
+    }
+  else                          /* delegate to system malloc */
+    mem = g_malloc (mem_size);
+  if (G_UNLIKELY (allocator->config.debug_blocks))
+    smc_notify_alloc (mem, mem_size);
+
+  TRACE (GLIB_SLICE_ALLOC((void*)mem, mem_size));
+
+  return mem;
+}
+
+/**
+ * g_slice_alloc0:
+ * @block_size: the number of bytes to allocate
+ *
+ * Allocates a block of memory via g_slice_alloc() and initializes
+ * the returned memory to 0. Note that the underlying slice allocation
+ * mechanism can be changed with the
+ * <link linkend="G_SLICE">G_SLICE=always-malloc</link>
+ * environment variable.
+ *
+ * Returns: a pointer to the allocated block
+ *
+ * Since: 2.10
+ */
+gpointer
+g_slice_alloc0 (gsize mem_size)
+{
+  gpointer mem = g_slice_alloc (mem_size);
+  if (mem)
+    memset (mem, 0, mem_size);
+  return mem;
+}
+
+/**
+ * g_slice_copy:
+ * @block_size: the number of bytes to allocate
+ * @mem_block: the memory to copy
+ *
+ * Allocates a block of memory from the slice allocator
+ * and copies @block_size bytes into it from @mem_block.
+ *
+ * Returns: a pointer to the allocated memory block
+ *
+ * Since: 2.14
+ */
+gpointer
+g_slice_copy (gsize         mem_size,
+              gconstpointer mem_block)
+{
+  gpointer mem = g_slice_alloc (mem_size);
+  if (mem)
+    memcpy (mem, mem_block, mem_size);
+  return mem;
+}
+
+/**
+ * g_slice_free1:
+ * @block_size: the size of the block
+ * @mem_block: a pointer to the block to free
+ *
+ * Frees a block of memory.
+ *
+ * The memory must have been allocated via g_slice_alloc() or
+ * g_slice_alloc0() and the @block_size has to match the size
+ * specified upon allocation. Note that the exact release behaviour
+ * can be changed with the
+ * <link linkend="G_DEBUG">G_DEBUG=gc-friendly</link> environment
+ * variable, also see <link linkend="G_SLICE">G_SLICE</link> for
+ * related debugging options.
+ *
+ * Since: 2.10
+ */
+void
+g_slice_free1 (gsize    mem_size,
+               gpointer mem_block)
+{
+  gsize chunk_size = P2ALIGN (mem_size);
+  guint acat = allocator_categorize (chunk_size);
+  if (G_UNLIKELY (!mem_block))
+    return;
+  if (G_UNLIKELY (allocator->config.debug_blocks) &&
+      !smc_notify_free (mem_block, mem_size))
+    abort();
+  if (G_LIKELY (acat == 1))             /* allocate through magazine layer */
+    {
+      ThreadMemory *tmem = thread_memory_from_self();
+      guint ix = SLAB_INDEX (allocator, chunk_size);
+      if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
+        {
+          thread_memory_swap_magazines (tmem, ix);
+          if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
+            thread_memory_magazine2_unload (tmem, ix);
+        }
+      if (G_UNLIKELY (g_mem_gc_friendly))
+        memset (mem_block, 0, chunk_size);
+      thread_memory_magazine2_free (tmem, ix, mem_block);
+    }
+  else if (acat == 2)                   /* allocate through slab allocator */
+    {
+      if (G_UNLIKELY (g_mem_gc_friendly))
+        memset (mem_block, 0, chunk_size);
+      g_mutex_lock (&allocator->slab_mutex);
+      slab_allocator_free_chunk (chunk_size, mem_block);
+      g_mutex_unlock (&allocator->slab_mutex);
+    }
+  else                                  /* delegate to system malloc */
+    {
+      if (G_UNLIKELY (g_mem_gc_friendly))
+        memset (mem_block, 0, mem_size);
+      g_free (mem_block);
+    }
+  TRACE (GLIB_SLICE_FREE((void*)mem_block, mem_size));
+}
+
+/**
+ * g_slice_free_chain_with_offset:
+ * @block_size: the size of the blocks
+ * @mem_chain:  a pointer to the first block of the chain
+ * @next_offset: the offset of the @next field in the blocks
+ *
+ * Frees a linked list of memory blocks of structure type @type.
+ *
+ * The memory blocks must be equal-sized, allocated via
+ * g_slice_alloc() or g_slice_alloc0() and linked together by a
+ * @next pointer (similar to #GSList). The offset of the @next
+ * field in each block is passed as third argument.
+ * Note that the exact release behaviour can be changed with the
+ * <link linkend="G_DEBUG">G_DEBUG=gc-friendly</link> environment
+ * variable, also see <link linkend="G_SLICE">G_SLICE</link> for
+ * related debugging options.
+ *
+ * Since: 2.10
+ */
+void
+g_slice_free_chain_with_offset (gsize    mem_size,
+                                gpointer mem_chain,
+                                gsize    next_offset)
+{
+  gpointer slice = mem_chain;
+  /* while the thread magazines and the magazine cache are implemented so that
+   * they can easily be extended to allow for free lists containing more free
+   * lists for the first level nodes, which would allow O(1) freeing in this
+   * function, the benefit of such an extension is questionable, because:
+   * - the magazine size counts will become mere lower bounds which confuses
+   *   the code adapting to lock contention;
+   * - freeing a single node to the thread magazines is very fast, so this
+   *   O(list_length) operation is multiplied by a fairly small factor;
+   * - memory usage histograms on larger applications seem to indicate that
+   *   the amount of released multi node lists is negligible in comparison
+   *   to single node releases.
+   * - the major performance bottle neck, namely g_private_get() or
+   *   g_mutex_lock()/g_mutex_unlock() has already been moved out of the
+   *   inner loop for freeing chained slices.
+   */
+  gsize chunk_size = P2ALIGN (mem_size);
+  guint acat = allocator_categorize (chunk_size);
+  if (G_LIKELY (acat == 1))             /* allocate through magazine layer */
+    {
+      ThreadMemory *tmem = thread_memory_from_self();
+      guint ix = SLAB_INDEX (allocator, chunk_size);
+      while (slice)
+        {
+          guint8 *current = slice;
+          slice = *(gpointer*) (current + next_offset);
+          if (G_UNLIKELY (allocator->config.debug_blocks) &&
+              !smc_notify_free (current, mem_size))
+            abort();
+          if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
+            {
+              thread_memory_swap_magazines (tmem, ix);
+              if (G_UNLIKELY (thread_memory_magazine2_is_full (tmem, ix)))
+                thread_memory_magazine2_unload (tmem, ix);
+            }
+          if (G_UNLIKELY (g_mem_gc_friendly))
+            memset (current, 0, chunk_size);
+          thread_memory_magazine2_free (tmem, ix, current);
+        }
+    }
+  else if (acat == 2)                   /* allocate through slab allocator */
+    {
+      g_mutex_lock (&allocator->slab_mutex);
+      while (slice)
+        {
+          guint8 *current = slice;
+          slice = *(gpointer*) (current + next_offset);
+          if (G_UNLIKELY (allocator->config.debug_blocks) &&
+              !smc_notify_free (current, mem_size))
+            abort();
+          if (G_UNLIKELY (g_mem_gc_friendly))
+            memset (current, 0, chunk_size);
+          slab_allocator_free_chunk (chunk_size, current);
+        }
+      g_mutex_unlock (&allocator->slab_mutex);
+    }
+  else                                  /* delegate to system malloc */
+    while (slice)
+      {
+        guint8 *current = slice;
+        slice = *(gpointer*) (current + next_offset);
+        if (G_UNLIKELY (allocator->config.debug_blocks) &&
+            !smc_notify_free (current, mem_size))
+          abort();
+        if (G_UNLIKELY (g_mem_gc_friendly))
+          memset (current, 0, mem_size);
+        g_free (current);
+      }
+}
+
+/* --- single page allocator --- */
+static void
+allocator_slab_stack_push (Allocator *allocator,
+                           guint      ix,
+                           SlabInfo  *sinfo)
+{
+  /* insert slab at slab ring head */
+  if (!allocator->slab_stack[ix])
+    {
+      sinfo->next = sinfo;
+      sinfo->prev = sinfo;
+    }
+  else
+    {
+      SlabInfo *next = allocator->slab_stack[ix], *prev = next->prev;
+      next->prev = sinfo;
+      prev->next = sinfo;
+      sinfo->next = next;
+      sinfo->prev = prev;
+    }
+  allocator->slab_stack[ix] = sinfo;
+}
+
+static gsize
+allocator_aligned_page_size (Allocator *allocator,
+                             gsize      n_bytes)
+{
+  gsize val = 1 << g_bit_storage (n_bytes - 1);
+  val = MAX (val, allocator->min_page_size);
+  return val;
+}
+
+static void
+allocator_add_slab (Allocator *allocator,
+                    guint      ix,
+                    gsize      chunk_size)
+{
+  ChunkLink *chunk;
+  SlabInfo *sinfo;
+  gsize addr, padding, n_chunks, color = 0;
+  gsize page_size = allocator_aligned_page_size (allocator, SLAB_BPAGE_SIZE (allocator, chunk_size));
+  /* allocate 1 page for the chunks and the slab */
+  gpointer aligned_memory = allocator_memalign (page_size, page_size - NATIVE_MALLOC_PADDING);
+  guint8 *mem = aligned_memory;
+  guint i;
+  if (!mem)
+    {
+      const gchar *syserr = "unknown error";
+#if HAVE_STRERROR
+      syserr = strerror (errno);
+#endif
+      mem_error ("failed to allocate %u bytes (alignment: %u): %s\n",
+                 (guint) (page_size - NATIVE_MALLOC_PADDING), (guint) page_size, syserr);
+    }
+  /* mask page address */
+  addr = ((gsize) mem / page_size) * page_size;
+  /* assert alignment */
+  mem_assert (aligned_memory == (gpointer) addr);
+  /* basic slab info setup */
+  sinfo = (SlabInfo*) (mem + page_size - SLAB_INFO_SIZE);
+  sinfo->n_allocated = 0;
+  sinfo->chunks = NULL;
+  /* figure cache colorization */
+  n_chunks = ((guint8*) sinfo - mem) / chunk_size;
+  padding = ((guint8*) sinfo - mem) - n_chunks * chunk_size;
+  if (padding)
+    {
+      color = (allocator->color_accu * P2ALIGNMENT) % padding;
+      allocator->color_accu += allocator->config.color_increment;
+    }
+  /* add chunks to free list */
+  chunk = (ChunkLink*) (mem + color);
+  sinfo->chunks = chunk;
+  for (i = 0; i < n_chunks - 1; i++)
+    {
+      chunk->next = (ChunkLink*) ((guint8*) chunk + chunk_size);
+      chunk = chunk->next;
+    }
+  chunk->next = NULL;   /* last chunk */
+  /* add slab to slab ring */
+  allocator_slab_stack_push (allocator, ix, sinfo);
+}
+
+static gpointer
+slab_allocator_alloc_chunk (gsize chunk_size)
+{
+  ChunkLink *chunk;
+  guint ix = SLAB_INDEX (allocator, chunk_size);
+  /* ensure non-empty slab */
+  if (!allocator->slab_stack[ix] || !allocator->slab_stack[ix]->chunks)
+    allocator_add_slab (allocator, ix, chunk_size);
+  /* allocate chunk */
+  chunk = allocator->slab_stack[ix]->chunks;
+  allocator->slab_stack[ix]->chunks = chunk->next;
+  allocator->slab_stack[ix]->n_allocated++;
+  /* rotate empty slabs */
+  if (!allocator->slab_stack[ix]->chunks)
+    allocator->slab_stack[ix] = allocator->slab_stack[ix]->next;
+  return chunk;
+}
+
+static void
+slab_allocator_free_chunk (gsize    chunk_size,
+                           gpointer mem)
+{
+  ChunkLink *chunk;
+  gboolean was_empty;
+  guint ix = SLAB_INDEX (allocator, chunk_size);
+  gsize page_size = allocator_aligned_page_size (allocator, SLAB_BPAGE_SIZE (allocator, chunk_size));
+  gsize addr = ((gsize) mem / page_size) * page_size;
+  /* mask page address */
+  guint8 *page = (guint8*) addr;
+  SlabInfo *sinfo = (SlabInfo*) (page + page_size - SLAB_INFO_SIZE);
+  /* assert valid chunk count */
+  mem_assert (sinfo->n_allocated > 0);
+  /* add chunk to free list */
+  was_empty = sinfo->chunks == NULL;
+  chunk = (ChunkLink*) mem;
+  chunk->next = sinfo->chunks;
+  sinfo->chunks = chunk;
+  sinfo->n_allocated--;
+  /* keep slab ring partially sorted, empty slabs at end */
+  if (was_empty)
+    {
+      /* unlink slab */
+      SlabInfo *next = sinfo->next, *prev = sinfo->prev;
+      next->prev = prev;
+      prev->next = next;
+      if (allocator->slab_stack[ix] == sinfo)
+        allocator->slab_stack[ix] = next == sinfo ? NULL : next;
+      /* insert slab at head */
+      allocator_slab_stack_push (allocator, ix, sinfo);
+    }
+  /* eagerly free complete unused slabs */
+  if (!sinfo->n_allocated)
+    {
+      /* unlink slab */
+      SlabInfo *next = sinfo->next, *prev = sinfo->prev;
+      next->prev = prev;
+      prev->next = next;
+      if (allocator->slab_stack[ix] == sinfo)
+        allocator->slab_stack[ix] = next == sinfo ? NULL : next;
+      /* free slab */
+      allocator_memfree (page_size, page);
+    }
+}
+
+/* --- memalign implementation --- */
+#ifdef HAVE_MALLOC_H
+#include <malloc.h>             /* memalign() */
+#endif
+
+/* from config.h:
+ * define HAVE_POSIX_MEMALIGN           1 // if free(posix_memalign(3)) works, <stdlib.h>
+ * define HAVE_COMPLIANT_POSIX_MEMALIGN 1 // if free(posix_memalign(3)) works for sizes != 2^n, <stdlib.h>
+ * define HAVE_MEMALIGN                 1 // if free(memalign(3)) works, <malloc.h>
+ * define HAVE_VALLOC                   1 // if free(valloc(3)) works, <stdlib.h> or <malloc.h>
+ * if none is provided, we implement malloc(3)-based alloc-only page alignment
+ */
+
+#if !(HAVE_COMPLIANT_POSIX_MEMALIGN || HAVE_MEMALIGN || HAVE_VALLOC)
+static GTrashStack *compat_valloc_trash = NULL;
+#endif
+
+static gpointer
+allocator_memalign (gsize alignment,
+                    gsize memsize)
+{
+  gpointer aligned_memory = NULL;
+  gint err = ENOMEM;
+#if     HAVE_COMPLIANT_POSIX_MEMALIGN
+  err = posix_memalign (&aligned_memory, alignment, memsize);
+#elif   HAVE_MEMALIGN
+  errno = 0;
+  aligned_memory = memalign (alignment, memsize);
+  err = errno;
+#elif   HAVE_VALLOC
+  errno = 0;
+  aligned_memory = valloc (memsize);
+  err = errno;
+#else
+  /* simplistic non-freeing page allocator */
+  mem_assert (alignment == sys_page_size);
+  mem_assert (memsize <= sys_page_size);
+  if (!compat_valloc_trash)
+    {
+      const guint n_pages = 16;
+      guint8 *mem = malloc (n_pages * sys_page_size);
+      err = errno;
+      if (mem)
+        {
+          gint i = n_pages;
+          guint8 *amem = (guint8*) ALIGN ((gsize) mem, sys_page_size);
+          if (amem != mem)
+            i--;        /* mem wasn't page aligned */
+          while (--i >= 0)
+            g_trash_stack_push (&compat_valloc_trash, amem + i * sys_page_size);
+        }
+    }
+  aligned_memory = g_trash_stack_pop (&compat_valloc_trash);
+#endif
+  if (!aligned_memory)
+    errno = err;
+  return aligned_memory;
+}
+
+static void
+allocator_memfree (gsize    memsize,
+                   gpointer mem)
+{
+#if     HAVE_COMPLIANT_POSIX_MEMALIGN || HAVE_MEMALIGN || HAVE_VALLOC
+  free (mem);
+#else
+  mem_assert (memsize <= sys_page_size);
+  g_trash_stack_push (&compat_valloc_trash, mem);
+#endif
+}
+
+static void
+mem_error (const char *format,
+           ...)
+{
+  const char *pname;
+  va_list args;
+  /* at least, put out "MEMORY-ERROR", in case we segfault during the rest of the function */
+  fputs ("\n***MEMORY-ERROR***: ", stderr);
+  pname = g_get_prgname();
+  fprintf (stderr, "%s[%ld]: GSlice: ", pname ? pname : "", (long)getpid());
+  va_start (args, format);
+  vfprintf (stderr, format, args);
+  va_end (args);
+  fputs ("\n", stderr);
+  abort();
+  _exit (1);
+}
+
+/* --- g-slice memory checker tree --- */
+typedef size_t SmcKType;                /* key type */
+typedef size_t SmcVType;                /* value type */
+typedef struct {
+  SmcKType key;
+  SmcVType value;
+} SmcEntry;
+static void             smc_tree_insert      (SmcKType  key,
+                                              SmcVType  value);
+static gboolean         smc_tree_lookup      (SmcKType  key,
+                                              SmcVType *value_p);
+static gboolean         smc_tree_remove      (SmcKType  key);
+
+
+/* --- g-slice memory checker implementation --- */
+static void
+smc_notify_alloc (void   *pointer,
+                  size_t  size)
+{
+  size_t adress = (size_t) pointer;
+  if (pointer)
+    smc_tree_insert (adress, size);
+}
+
+#if 0
+static void
+smc_notify_ignore (void *pointer)
+{
+  size_t adress = (size_t) pointer;
+  if (pointer)
+    smc_tree_remove (adress);
+}
+#endif
+
+static int
+smc_notify_free (void   *pointer,
+                 size_t  size)
+{
+  size_t adress = (size_t) pointer;
+  SmcVType real_size;
+  gboolean found_one;
+
+  if (!pointer)
+    return 1; /* ignore */
+  found_one = smc_tree_lookup (adress, &real_size);
+  if (!found_one)
+    {
+      fprintf (stderr, "GSlice: MemChecker: attempt to release non-allocated block: %p size=%" G_GSIZE_FORMAT "\n", pointer, size);
+      return 0;
+    }
+  if (real_size != size && (real_size || size))
+    {
+      fprintf (stderr, "GSlice: MemChecker: attempt to release block with invalid size: %p size=%" G_GSIZE_FORMAT " invalid-size=%" G_GSIZE_FORMAT "\n", pointer, real_size, size);
+      return 0;
+    }
+  if (!smc_tree_remove (adress))
+    {
+      fprintf (stderr, "GSlice: MemChecker: attempt to release non-allocated block: %p size=%" G_GSIZE_FORMAT "\n", pointer, size);
+      return 0;
+    }
+  return 1; /* all fine */
+}
+
+/* --- g-slice memory checker tree implementation --- */
+#define SMC_TRUNK_COUNT     (4093 /* 16381 */)          /* prime, to distribute trunk collisions (big, allocated just once) */
+#define SMC_BRANCH_COUNT    (511)                       /* prime, to distribute branch collisions */
+#define SMC_TRUNK_EXTENT    (SMC_BRANCH_COUNT * 2039)   /* key address space per trunk, should distribute uniformly across BRANCH_COUNT */
+#define SMC_TRUNK_HASH(k)   ((k / SMC_TRUNK_EXTENT) % SMC_TRUNK_COUNT)  /* generate new trunk hash per megabyte (roughly) */
+#define SMC_BRANCH_HASH(k)  (k % SMC_BRANCH_COUNT)
+
+typedef struct {
+  SmcEntry    *entries;
+  unsigned int n_entries;
+} SmcBranch;
+
+static SmcBranch     **smc_tree_root = NULL;
+
+static void
+smc_tree_abort (int errval)
+{
+  const char *syserr = "unknown error";
+#if HAVE_STRERROR
+  syserr = strerror (errval);
+#endif
+  mem_error ("MemChecker: failure in debugging tree: %s", syserr);
+}
+
+static inline SmcEntry*
+smc_tree_branch_grow_L (SmcBranch   *branch,
+                        unsigned int index)
+{
+  unsigned int old_size = branch->n_entries * sizeof (branch->entries[0]);
+  unsigned int new_size = old_size + sizeof (branch->entries[0]);
+  SmcEntry *entry;
+  mem_assert (index <= branch->n_entries);
+  branch->entries = (SmcEntry*) realloc (branch->entries, new_size);
+  if (!branch->entries)
+    smc_tree_abort (errno);
+  entry = branch->entries + index;
+  g_memmove (entry + 1, entry, (branch->n_entries - index) * sizeof (entry[0]));
+  branch->n_entries += 1;
+  return entry;
+}
+
+static inline SmcEntry*
+smc_tree_branch_lookup_nearest_L (SmcBranch *branch,
+                                  SmcKType   key)
+{
+  unsigned int n_nodes = branch->n_entries, offs = 0;
+  SmcEntry *check = branch->entries;
+  int cmp = 0;
+  while (offs < n_nodes)
+    {
+      unsigned int i = (offs + n_nodes) >> 1;
+      check = branch->entries + i;
+      cmp = key < check->key ? -1 : key != check->key;
+      if (cmp == 0)
+        return check;                   /* return exact match */
+      else if (cmp < 0)
+        n_nodes = i;
+      else /* (cmp > 0) */
+        offs = i + 1;
+    }
+  /* check points at last mismatch, cmp > 0 indicates greater key */
+  return cmp > 0 ? check + 1 : check;   /* return insertion position for inexact match */
+}
+
+static void
+smc_tree_insert (SmcKType key,
+                 SmcVType value)
+{
+  unsigned int ix0, ix1;
+  SmcEntry *entry;
+
+  g_mutex_lock (&smc_tree_mutex);
+  ix0 = SMC_TRUNK_HASH (key);
+  ix1 = SMC_BRANCH_HASH (key);
+  if (!smc_tree_root)
+    {
+      smc_tree_root = calloc (SMC_TRUNK_COUNT, sizeof (smc_tree_root[0]));
+      if (!smc_tree_root)
+        smc_tree_abort (errno);
+    }
+  if (!smc_tree_root[ix0])
+    {
+      smc_tree_root[ix0] = calloc (SMC_BRANCH_COUNT, sizeof (smc_tree_root[0][0]));
+      if (!smc_tree_root[ix0])
+        smc_tree_abort (errno);
+    }
+  entry = smc_tree_branch_lookup_nearest_L (&smc_tree_root[ix0][ix1], key);
+  if (!entry ||                                                                         /* need create */
+      entry >= smc_tree_root[ix0][ix1].entries + smc_tree_root[ix0][ix1].n_entries ||   /* need append */
+      entry->key != key)                                                                /* need insert */
+    entry = smc_tree_branch_grow_L (&smc_tree_root[ix0][ix1], entry - smc_tree_root[ix0][ix1].entries);
+  entry->key = key;
+  entry->value = value;
+  g_mutex_unlock (&smc_tree_mutex);
+}
+
+static gboolean
+smc_tree_lookup (SmcKType  key,
+                 SmcVType *value_p)
+{
+  SmcEntry *entry = NULL;
+  unsigned int ix0 = SMC_TRUNK_HASH (key), ix1 = SMC_BRANCH_HASH (key);
+  gboolean found_one = FALSE;
+  *value_p = 0;
+  g_mutex_lock (&smc_tree_mutex);
+  if (smc_tree_root && smc_tree_root[ix0])
+    {
+      entry = smc_tree_branch_lookup_nearest_L (&smc_tree_root[ix0][ix1], key);
+      if (entry &&
+          entry < smc_tree_root[ix0][ix1].entries + smc_tree_root[ix0][ix1].n_entries &&
+          entry->key == key)
+        {
+          found_one = TRUE;
+          *value_p = entry->value;
+        }
+    }
+  g_mutex_unlock (&smc_tree_mutex);
+  return found_one;
+}
+
+static gboolean
+smc_tree_remove (SmcKType key)
+{
+  unsigned int ix0 = SMC_TRUNK_HASH (key), ix1 = SMC_BRANCH_HASH (key);
+  gboolean found_one = FALSE;
+  g_mutex_lock (&smc_tree_mutex);
+  if (smc_tree_root && smc_tree_root[ix0])
+    {
+      SmcEntry *entry = smc_tree_branch_lookup_nearest_L (&smc_tree_root[ix0][ix1], key);
+      if (entry &&
+          entry < smc_tree_root[ix0][ix1].entries + smc_tree_root[ix0][ix1].n_entries &&
+          entry->key == key)
+        {
+          unsigned int i = entry - smc_tree_root[ix0][ix1].entries;
+          smc_tree_root[ix0][ix1].n_entries -= 1;
+          g_memmove (entry, entry + 1, (smc_tree_root[ix0][ix1].n_entries - i) * sizeof (entry[0]));
+          if (!smc_tree_root[ix0][ix1].n_entries)
+            {
+              /* avoid useless pressure on the memory system */
+              free (smc_tree_root[ix0][ix1].entries);
+              smc_tree_root[ix0][ix1].entries = NULL;
+            }
+          found_one = TRUE;
+        }
+    }
+  g_mutex_unlock (&smc_tree_mutex);
+  return found_one;
+}
+
+#ifdef G_ENABLE_DEBUG
+void
+g_slice_debug_tree_statistics (void)
+{
+  g_mutex_lock (&smc_tree_mutex);
+  if (smc_tree_root)
+    {
+      unsigned int i, j, t = 0, o = 0, b = 0, su = 0, ex = 0, en = 4294967295u;
+      double tf, bf;
+      for (i = 0; i < SMC_TRUNK_COUNT; i++)
+        if (smc_tree_root[i])
+          {
+            t++;
+            for (j = 0; j < SMC_BRANCH_COUNT; j++)
+              if (smc_tree_root[i][j].n_entries)
+                {
+                  b++;
+                  su += smc_tree_root[i][j].n_entries;
+                  en = MIN (en, smc_tree_root[i][j].n_entries);
+                  ex = MAX (ex, smc_tree_root[i][j].n_entries);
+                }
+              else if (smc_tree_root[i][j].entries)
+                o++; /* formerly used, now empty */
+          }
+      en = b ? en : 0;
+      tf = MAX (t, 1.0); /* max(1) to be a valid divisor */
+      bf = MAX (b, 1.0); /* max(1) to be a valid divisor */
+      fprintf (stderr, "GSlice: MemChecker: %u trunks, %u branches, %u old branches\n", t, b, o);
+      fprintf (stderr, "GSlice: MemChecker: %f branches per trunk, %.2f%% utilization\n",
+               b / tf,
+               100.0 - (SMC_BRANCH_COUNT - b / tf) / (0.01 * SMC_BRANCH_COUNT));
+      fprintf (stderr, "GSlice: MemChecker: %f entries per branch, %u minimum, %u maximum\n",
+               su / bf, en, ex);
+    }
+  else
+    fprintf (stderr, "GSlice: MemChecker: root=NULL\n");
+  g_mutex_unlock (&smc_tree_mutex);
+  
+  /* sample statistics (beast + GSLice + 24h scripted core & GUI activity):
+   *  PID %CPU %MEM   VSZ  RSS      COMMAND
+   * 8887 30.3 45.8 456068 414856   beast-0.7.1 empty.bse
+   * $ cat /proc/8887/statm # total-program-size resident-set-size shared-pages text/code data/stack library dirty-pages
+   * 114017 103714 2354 344 0 108676 0
+   * $ cat /proc/8887/status 
+   * Name:   beast-0.7.1
+   * VmSize:   456068 kB
+   * VmLck:         0 kB
+   * VmRSS:    414856 kB
+   * VmData:   434620 kB
+   * VmStk:        84 kB
+   * VmExe:      1376 kB
+   * VmLib:     13036 kB
+   * VmPTE:       456 kB
+   * Threads:        3
+   * (gdb) print g_slice_debug_tree_statistics ()
+   * GSlice: MemChecker: 422 trunks, 213068 branches, 0 old branches
+   * GSlice: MemChecker: 504.900474 branches per trunk, 98.81% utilization
+   * GSlice: MemChecker: 4.965039 entries per branch, 1 minimum, 37 maximum
+   */
+}
+#endif /* G_ENABLE_DEBUG */